700,000 Year Old Horse Genome Decoded: New World Record in DNA Research

A new world record has been set in DNA research. Scientists have sequenced the oldest genome yet--a whopping 700,000 years old. What does this particular genome belong to? Apparently it's from the remains of a prehistoric wild horse.

Hundreds of thousands of years ago, this wild horse once roamed the icy reaches of Yukon, Canada. It met its unfortunate end and then was preserved in permafrost until the present day. Scientists eventually unearthed the creature, discovering that it contained short pieces of DNA molecules preserved in bone-remnants. Yet actually sequencing this DNA was no easy task.

DNA molecules can survive in fossils long after an organism dies--usually as short pieces. These short pieces then have to be assembled back together, rather like a puzzle. Although it's never certain, sometimes enough molecules can survive so that the full genome sequence of an extinct species can be resurrected.

In this specific case, the researchers compared the genome of the 700,000 year old horse with the genomes of a 43,000 year old horse. Then they compared it to six present day horses and a donkey. By doing so, the scientists could estimate how fast mutations accumulated through time and could calibrate a genome-wide mutation rate. In other words, they could see how quickly the modern horse evolved.

So what did they find? It turns out that the last common ancestor of all modern equids--which include horses, donkeys and zebras--was living about 4 to 4.5 million years ago. This means that the evolutionary radiation underlying the origin of these creatures reaches back in time twice as long as previously thought. In addition, the scientists discovered that there were multiple episodes of severe demographic fluctuation in horse history, aligning with major climatic changes, such as the Last Glacial Maximum about 20,000 years ago.

They didn't just find out this information, though. The researchers also learned something about the so-called Przewalski's Horse from the Mongolian steppes. This horse population was discovered by the Western world in the second half of the nineteenth century. This population subsequently became threatened and then almost extinct in the 1970s. It shows striking physical differences compared to domesticated horses and even an extra pair of chromosomes. It turns out, though, that this horse became isolated from the lineage leading to our domestic horse about 50,000 years ago.

The findings are huge for DNA research and for better understanding the history of the horse. They also show that it's possible to sequence a genome that's 700,000 years old--no small feat. This could lead to further research into other genomes that are as old--or perhaps even older.

The findings are published in the journal Nature.